The common flashlights can be classified into focusing flashlights and unfocusing flashlights depending on whether the flashlights can focus or not. The focusing flashlights generally perform the focusing by rotating the housing head or the front cover to allow the luminous point of the bulb and the focus of the parabolic reflector to coincide. However, this kind of focusing flashlight has a disadvantage that when the user rotates the housing head or the front cover unconsciously and the focus of the reflector mismatches with the lighting point of the bulb, the lights scatter, and a readjustment of focusing is needed. Unfocusing flashlights fix the relative positions of the reflector and the bulb. The bulbs of some unfocusing flashlights cannot be replaced whereas some others can be replaced. Even if the bulb can be replaced, the flashlight with the replaced bulb is not focused because the actual height of the filament in each bulb is somewhat variable.